The present invention relates to cutting tools for cutting a workpiece and methods of cutting a workpiece in multiple directions with substantially equal cutting capacity in all cutting directions. The cutting tool and method of the present invention are ideally suited for complex cutting operations, requiring either sequential or simultaneous cutting in at least two axes.
Due to advances in cutting machine technology, such as for example computer numerical controlled machines or CNC machines, a need has arisen for advanced cutting tools capable of complex metal removal operations in multiple directions. Multiple directional cutting may take many forms, as for example, forming a slot in a workpiece with an axial cut followed by a lateral cut. To cut a ramp into a workpiece, simultaneous metal removal along at least two axes is required, etc. All of these cutting possibilities require a combination of known cutting methods to accomplish the finished cut. For example, the forming of a slot requires drilling to a predetermined depth and then milling laterally from the drilled hole.
As is well known, there are a variety of cutting tools available for making the individual cuts that when combined result in complex cuts. Typically, the above example of a slot is formed by drilling into the workpiece with a drill bit or a hole cutter and then inserting an end mill into the hole formed to make the laterally extending slot.
There are numerous examples of hole cutters, drills and milling cutters for making these individual cuts. The inventor of the present invention is a leading innovator in cutting tool technology with numerous patents relating to cutting tools for cutting holes in a workpiece. Other examples of some of his cutting tools are found in U.S. Pat. Nos. 3,765,789; 3,860,354; U.S. Pat. Nos. Re. 28,416; U.S. Pat. Nos. 4,322,187; 4,452,554; 4,538,944; and 4,632,610. All of these cutting tools have met with considerable success in the United States and abroad for use in forming a hole in a workpiece. Examples of recent developments in drill bits for use in forming holes can be found in U.S. Pat. Nos. 4,687,388, issued to Yokota et al., and 4,373,839, issued to Negishi et al. An example of an end mill for milling a slot can be found in U.S. Pat. No. 2,129,417 issued to Gase.
The problem with the above cutting tools in complex cutting operations is their inability to cut along multiple axes either sequentially or simultaneously. They are designed to cut along a single axis, not along multiple axes. Typically, they cannot be used to cut a ramp because of their single axis capability. Further, to cut a slot, the hole cutter or drill would have to be removed from the hole after the hole is formed and replaced with an end mill to complete the slot. Although this is a common method of forming slots, it is time consuming to change these tools. The necessity of having to change tools when a new axis is selected greatly hinders the performance capabilities of the CNC machine.
There have been attempts to develop cutters that can cut in multiple directions. U.S. Pat. No. 4,265,574 issued to Eckle on May 5, 1981 discloses a combined boring and milling tool having at least three triangularly-shaped turnable cutter blades intended for forming slots or grooves in a workpiece. The cutting blades or edges are mounted at the free end of the cutting tool and at the periphery of the tool. The disclosed tool can be used to first drill to a predetermined depth then, by movement of the tool perpendicular to the first cut, a slot can be milled at full depth.
Although this tool would appear to work as both a drill and an end mill, there are several disadvantages. First, the cutting tool of Eckle only has one cutting edge cutting each path through the workpiece. This results in a slow cutting feed rate. Second, the cutting edge on the face of the Eckle tool extends from the outer periphery of the tool past the axis of rotation of the tool. As will be understood, as the cutting edge approaches the center or rotational axis of the tool, the speed of the cutting edge approaches zero. At the center of the tool, the cutting speed is zero which is commonly referred to as the "dead spot." At the dead spot, due to the cutting speed being zero, the cutter does not cut the material but cold forms it, which consumes excessive horsepower, creates excessive tool pressures, and inhibits the rate at which the tool can axially penetrate the material.
A further attempt to provide a multidirectional cutting tool is disclosed in Allaire et al., U.S. Pat. No. 4,618,296, issued Oct. 21, 1986. Allaire et al. discloses a cutting tool capable of omni-directional machining of a workpiece. The cutting tool is a ball-nosed end mill with a cylindrical shape terminating in a spherically-shaped cutting end with recesses shaped for receipt of at least two indexable cutting inserts. Each insert is mounted in a "lay-down fashion" to provide a portion of an effective overall arcuate cutting edge. The cutting zones of each insert have the form of an equilateral polygon bounded by planar flanks with each flank intersecting a convex portion of a major face of an insert to form an arcuate cutting edge. The convex major face portion forms the clearance face and the planar flank portion forms the rake face for each associated arcuate cutting edge.
The Allaire et al. cutting tool has several disadvantages. It would appear that the Allaire et al. cutting tool is capable of drilling or boring; however, it is extremely limited as to the depth of penetration due to the placement of the cutting inserts 11 and 12. Further, Allaire et al. suffers the same dead spot problem as Eckle discussed above. As best illustrated in FIG. 2 of the Allaire et al. patent, the cutting edge 10 extends to the axis of rotation of the cutter defining a center dead spot. As with Eckle, this consumes horsepower and creates excessive tool pressures which inhibit the rate at which the tool can axially penetrate the workpiece. Also, Allaire et al. has only one cutting edge for cutting each path similar to Eckle. Still further, the Allaire et al. tool has no advantages in end cutting over state-of-the-art standard center cutting end mills. In fact, Allaire et al. may be less efficient due to the high cutting angles near full diameter of the cutter and the lack of chip passages.
Kondo et al., U.S. Pat. No. 4,564,321, issued Jan. 14, 1986, discloses an end-milling cutter with drilling capability. The Kondo et al. cutter has replaceable inserts for the cutting edges and is capable of cutting holes at greater depths. The end mill carries at least two peripheral-cutting inserts for peripheral milling, an inner drilling insert for cutting a radially inward portion of a hole, and an outer drilling insert for cutting a radially outward portion of the hole. The Kondo et al. cutter also includes flutes with the peripheral-cutting inserts disposed in a staggered manner alternately in the first and second flute surfaces. Further, Kondo et al. has an oil passage 11 formed through radially central portions of the body and shank. The oil passage 11, which is a channel for introducing coolant, is open at the end of the end mill 2 to direct the coolant flow to the end of body 4.
However, as with the previously discussed cutters, the Kondo et al. cutting tool has only one edge cutting each path. Again, this slows the cutting capability. The face cutting edge 26 of Kondo et al. extends to the axis of rotation of the cutting tool which creates a dead spot with the same disadvantages discussed above. In view of these difficulties, although the tool should work as both a drill and an end mill, both capacities are limited.
What is needed is a cutting tool which can cut in multiple directions, either sequentially or simultaneously, with equal cutting capacity in all directions, so that there is substantially equal metal removal efficiency in all directions. Also, a cutting tool is needed which has multiple cutting edges that cut the same path for both end-cutting and side-cutting, as opposed to one cutting a edge cutting a single path as found in the above cutters. Further, a cutting tool is needed which does not have a dead spot and which has a coolant passage for supplying coolant to the cutting edges to dissipate generated heat.